Method of measuring a parameter of interest, inspection apparatus, lithographic system and device manufacturing method

Abstract

A method of measuring a parameter of interest relating to a structure formed by a process on a substrate, and associated apparatuses. The method includes measuring the structure with measurement radiation including a first illumination acquisition setting (determining one or more selected from: a wavelength, a polarization or an incident angle of the measurement radiation) to obtain a first measurement value for the structure. The method further includes estimating, by applying a correction model to the first measurement value, at least a second measurement value for the structure corresponding to measurement of the structure with a second illumination acquisition setting different from the first illumination acquisition setting.

The invention claimed is: 
     
       1. A method of measuring a parameter of interest relating to a structure formed by a process on a substrate, the method comprising:
 measuring the structure with measurement radiation comprising a first illumination acquisition setting to obtain a first measurement value for the structure corresponding to measurement of the structure with the first illumination acquisition setting, wherein the illumination acquisition setting determines one or more selected from: a wavelength, a polarization or an incident angle of the measurement radiation; and 
 estimating, by applying a correction model to the first measurement value, at least a second measurement value for the structure corresponding to measurement of the structure with a second illumination acquisition setting different from the first illumination acquisition setting. 
 
     
     
       2. The method of  claim 1 , wherein the correction model comprises a position-dependent correction model dependent on the position of the structure on the substrate. 
     
     
       3. The method of  claim 1 , comprising a calibration phase for determining the correction model. 
     
     
       4. The method of  claim 1 , wherein the correction model comprises a statistical correlation model relating measurements of the structure using the first illumination acquisition setting to measurements of the structure using the second illumination acquisition setting. 
     
     
       5. The method of  claim 3 , wherein the calibration phase comprises measuring a calibration set of structures on the substrate with,at least measurement radiation comprising the first illumination acquisition setting and with at least measurement radiation comprising the second illumination acquisition setting. 
     
     
       6. The method of  claim 5 , wherein the calibration phase comprises:
 measuring the calibration set of structures on the substrate with measurement radiation comprising one or more further illumination acquisition settings, additional to the first illumination acquisition setting and second illumination acquisition setting, 
 wherein the correction model comprises a statistical correlation model relating measurements of the structure using the first illumination acquisition setting to measurements of the structure using the second illumination acquisition setting and to each of the one or more further illumination acquisition settings, and 
 wherein the estimating further comprises comprising estimating, by applying the correction model to the first measurement value, a further measurement value for the structure corresponding to each further illumination acquisition setting. 
 
     
     
       7. The method of  claim 5 , wherein the measuring and estimating are performed for each structure of a measurement set of structures on the substrate, and wherein the calibration set of structures is a subset of the measurement set of structures. 
     
     
       8. The method of  claim 7 , wherein the structures of the calibration set are distributed over intrafield locations of the measurement set. 
     
     
       9. The method of  claim 8 , wherein the specific structures included in the calibration set corresponding to a particular intrafield location are randomly selected. 
     
     
       10. The method of  claim 3 , wherein the calibration phase is performed on a first substrate of a lot and the measuring and estimating are performed for one or more of the remaining substrates of the lot. 
     
     
       11. The method of  claim 3 , wherein the calibration phase comprises determining a function which relates first measurement data corresponding to the first illumination acquisition setting to at least second measurement data corresponding to the second illumination acquisition setting. 
     
     
       12. The method of  claim 11 , wherein the function comprises determining a canonical correlation between the first measurement data and second measurement data. 
     
     
       13. The method of  claim 11 , wherein the first measurement data and second measurement data each comprise, for each structure measured in the calibration phase, at least one intensity metric related to the intensity of a selected part of diffracted radiation following diffraction by the structure being measured, and a position metric relating to the position of the structure on the substrate. 
     
     
       14. The method of  claim 1 , wherein the parameter of interest is related to asymmetry in the structure, and the measuring comprises:
 forming and detecting a first image of the structure while illuminating the structure with the measurement radiation, the first image being formed using a first selected part of diffracted radiation; 
 forming and detecting a second image of the structure while illuminating the structure with the measurement radiation, the second image being formed using a second selected part of diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the structure; and 
 calculating a measurement of asymmetry in the structure based on intensity values derived from the detected first and second images. 
 
     
     
       15. The method of  claim 1 , wherein the parameter of interest is overlay or focus or dose. 
     
     
       16. An inspection apparatus configured to measure a parameter of interest relating to a structure formed by a process on a substrate, the inspection apparatus being configured to perform the method of  claim 1 . 
     
     
       17. The inspection apparatus of  claim 16 , comprising:
 an illumination and detection arrangement operable in a first illumination acquisition setting to perform the measuring; and 
 a controller programmed to perform the estimating. 
 
     
     
       18. A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including inspecting at least one periodic structure formed as part of or beside the device pattern on at least one of the substrates using the inspection method of  claim 1 , and controlling the lithographic process for later substrates in accordance with a result of the inspection method. 
     
     
       19. A non-transitory computer program product comprising machine readable instructions therein, the instructions, upon execution by a programmable processing device, configured to cause the programmable processing device to at least:
 obtain measurements of a structure formed by a process on a substrate with measurement radiation comprising a first illumination acquisition setting to obtain a first measurement value for the structure corresponding to measurement of the structure with the first illumination acquisition setting, wherein the illumination acquisition setting determines one or more selected from: a wavelength, a polarization or an incident angle of the measurement radiation; and 
 estimate, by application of a correction model to the first measurement value, at least a second measurement value for the structure corresponding to measurement of the structure with a second illumination acquisition setting different from the first illumination acquisition setting. 
 
     
     
       20. A lithographic system comprising:
 a lithographic apparatus comprising:
 an illumination optical system arranged to illuminate a pattern; 
 a projection optical system arranged to project an image of the pattern onto a substrate; and 
 
 the non-transitory computer program product of  claim 19 , 
 wherein the lithographic apparatus is arranged to use the results from the non-transitory computer program product in applying the pattern to further substrates.